Acceleration sensor

Abstract

This acceleration sensor comprises a device layer including a weight part, a fixing part, and a vibrator each disposed on an intersection plane intersecting with a sensitivity axis direction, and a housing for housing the device layer, the acceleration sensor detecting acceleration in the sensitivity axis direction. The weight part has a rotation axis extending in a first orthogonal axis direction orthogonal to the sensitivity axis direction, and is held by the housing so as to rotate around the rotation axis by receiving acceleration in the sensitivity axis direction. The fixing part is fixed to the housing via an anchor part protruding from the housing in the sensitivity axis direction. The vibrator is connected to the weight part at one end portion in a second orthogonal axis direction orthogonal to the sensitive axis direction and the first orthogonal axis direction, is connected to the fixing part at the other end portion opposite to the one end portion in the second orthogonal axis direction, and is configured such that the resonance frequency changes on the basis of bending stress according to displacement of the weight part. When the weight part is in a stationary state, the rotation axis of the weight part is separated in the sensitivity axis direction from a plane extending along the intersection surface from a neutral plane with respect to the bending stress of the vibrator.

Description

Acceleration sensor

[0001] The present invention relates to an acceleration sensor.

[0002] As acceleration sensors, a capacitance-type acceleration sensor that detects acceleration based on a change in capacitance formed by a movable part, a frequency modulation-type acceleration sensor that detects acceleration based on a change in the resonance frequency of a vibrator connected to a movable part, etc. are used.

[0003] For example, in Patent Document 1, there is an element including a frame, a pair of diaphragm plates provided opposite to each other linearly on this frame, a support body that holds one end side of each diaphragm plate in proximity, and a holding part that holds this support body slidably in a linear direction. Due to the acceleration propagated to the support body through the holding part of this element, the diaphragm plates expand and contract, and an acceleration is detected from the change in the natural vibration frequency of this diaphragm plate. A vibration-type piezoelectric acceleration sensor is disclosed. [[ID=U11]]

[0004] Japanese Patent Application Laid-Open No. 2005-249446

[0005] According to the acceleration sensor described in Patent Document 1, when receiving an in-plane direction acceleration, a so-called reverse-phase deformation occurs where tensile strain occurs in one of the pair of diaphragm plates and compressive strain occurs in the other. Therefore, by reading the difference in the change in the natural vibration frequency, the in-plane direction acceleration of the element can be detected with high sensitivity. However, when receiving an out-of-plane direction acceleration, a so-called in-phase deformation occurs where tensile strain occurs in both of the pair of diaphragm plates. Therefore, there is a problem that the out-of-plane direction acceleration cannot be detected because the frequency change amounts of the pair of diaphragm plates cancel each other out in the difference in the change in the natural vibration frequency.

[0006] The present invention has been made in view of such circumstances, and an object thereof is to provide an acceleration sensor capable of detecting an out-of-plane direction acceleration.

[0007] An acceleration sensor according to one aspect of the present invention comprises a device layer including a weight portion, a fixed portion, and a vibrator, which are respectively arranged on intersecting surfaces that intersect with the sensitivity axis direction, and a housing that houses the device layer, and is an acceleration sensor for detecting acceleration in the direction of the sensitivity axis direction. The weight portion has a rotation axis extending in a first orthogonal axis direction perpendicular to the sensitivity axis direction, and is held in the housing so as to rotate about the rotation axis when subjected to acceleration in the direction of the sensitivity axis direction. The fixed portion is fixed to the housing via an anchor portion that protrudes from the housing in the direction of the sensitivity axis direction. The vibrator is connected to the weight portion at one end in the direction of the sensitivity axis direction and a second orthogonal axis direction perpendicular to the first orthogonal axis direction, and is connected to the fixed portion at the other end opposite to the one end in the second orthogonal axis direction, and is configured such that the resonant frequency changes based on the bending stress corresponding to the displacement of the weight portion. When the weight portion is in a stationary state, the rotation axis of the weight portion is away in the direction of the sensitivity axis from a plane that extends along the intersecting surface from the neutral plane with respect to the bending stress of the vibrator.

[0008] According to the present invention, it is possible to provide an acceleration sensor capable of detecting acceleration in the out-of-plane direction.

[0009] This is an exploded perspective view of the acceleration sensor according to the first embodiment. This is a plan view of the device layer in the acceleration sensor according to the first embodiment. This is a cross-sectional view of the acceleration sensor according to the first embodiment. This is a cross-sectional view of the acceleration sensor according to the first embodiment. This is a cross-sectional view of the device layer in the basic state. This is a cross-sectional view of the device layer in the detection state. This is a diagram showing the simulation results of the stress distribution in the first embodiment. This is a cross-sectional view of the device layer according to the comparative example in the detection state. This is a diagram showing the simulation results of the stress distribution in the comparative example. This is a cross-sectional view of the device layer according to the second embodiment. This is a cross-sectional view of the acceleration sensor according to the third embodiment. This is a cross-sectional view of the acceleration sensor according to the third embodiment. This is a plan view of the acceleration sensor according to the fourth embodiment in the basic state. This is a plan view of the acceleration sensor according to the fourth embodiment in the detection state.

[0010] Embodiments of the present invention are described below. In the following drawings, identical or similar components are denoted by identical or similar reference numerals. The drawings are illustrative, and the dimensions and shapes of each part are schematic; the technical scope of the present invention should not be limited to these embodiments.

[0011] Each drawing may include a Cartesian coordinate system consisting of the X, Y, and Z axes for convenience, in order to clarify the relationships between the drawings and to help understand the positional relationships of each component. The X, Y, and Z axes correspond to each other in each drawing.

[0012] In the following explanation, the direction parallel to the X-axis is referred to as the "X-axis direction," the direction parallel to the Y-axis as the "Y-axis direction," and the direction parallel to the Z-axis as the "Z-axis direction." Furthermore, the direction of the arrowheads for the X, Y, and Z axes is considered "positive" or "+ (plus)," and the direction opposite to the arrow is considered "negative" or "- (minus)." For convenience, the +Z-axis direction is described as upward and the -Z-axis direction as downward, but the vertical orientation of the acceleration sensor 1 is not limited. Also, the plane specified by the X and Z axes is referred to as the ZX plane, and the direction parallel to the ZX plane is referred to as the ZX plane direction. The same applies to the planes specified by the other axes.

[0013] <First Embodiment>

[0014] First, the configuration of the acceleration sensor 1 in its basic state according to the first embodiment will be described with reference to Figures 1 to 4. Figure 1 is an exploded perspective view of the acceleration sensor 1 according to the first embodiment. Figure 2 is a plan view of the device layer 100 in the acceleration sensor 1 according to the first embodiment. Figure 3 is a cross-sectional view of the acceleration sensor 1 according to the first embodiment. Figure 4 is a cross-sectional view of the acceleration sensor 1 according to the first embodiment. Note that Figure 3 is a cross-sectional view of the acceleration sensor 1 in its basic state, parallel to the YZ plane along the line A-A. Figure 4 is a cross-sectional view of the acceleration sensor 1 in its basic state, parallel to the ZX plane along the line B-B. "Basic state" refers to the stationary state in which the acceleration sensor 1 is not receiving acceleration.

[0015] The acceleration sensor 1 is a frequency-modulated acceleration sensor. The sensitivity axis of the acceleration sensor 1 is the Z-axis, and the acceleration sensor 1 detects acceleration in the Z-axis direction. The Z-axis is an example of the sensitivity axis of the acceleration sensor 1, the X-axis and Y-axis are examples of orthogonal axes perpendicular to the sensitivity axis, and the XY plane is an example of an orthogonal plane perpendicular to the sensitivity axis. The Z-axis direction is an example of the sensitivity axis direction, the Y-axis direction is an example of the first orthogonal axis direction, and the X-axis direction is an example of the second orthogonal axis direction. A plane that intersects the sensitivity axis is called an intersecting plane. An intersecting plane includes an orthogonal plane and is, for example, a plane whose angle with the sensitivity axis is 45 degrees or more and 135 degrees or less (90 degrees ± 45 degrees). The angle between the intersecting plane and the sensitivity axis is preferably 60 degrees or more and 120 degrees or less (90 degrees ± 30 degrees), more preferably 70 degrees or more and 110 degrees or less (90 degrees ± 20 degrees), and still more preferably 80 degrees or more and 100 degrees or less (90 degrees ± 10 degrees).

[0016] As shown in Figure 1, the acceleration sensor 1 comprises a device layer 100, a lower housing 170, and an upper housing 180. The lower housing 170 and the upper housing 180 are connected to each other via a frame portion 150 of the device layer 100, which will be described later, and constitute a housing 190 that houses the device layer 100.

[0017] As shown in Figure 2, the device layer 100 includes a weight portion 110, a fixing portion 120, a vibrator 130, a connecting portion 140, and a frame portion 150. Each of the weight portion 110, fixing portion 120, vibrator 130, connecting portion 140, and frame portion 150 is arranged on an intersecting surface.

[0018] The weight portion 110 is a plate-shaped member having a pair of main surfaces. In its basic state, the main surfaces of the weight portion 110 extend in the XY plane direction. When viewed from a plan view from the Z axis direction, which is the sensitivity axis (hereinafter simply referred to as "plan view"), the weight portion 110 is provided in a rectangular frame shape having a pair of long sides extending in the X axis direction and a pair of short sides extending in the Y axis direction. The weight portion 110 is provided between the fixing portion 120 and the frame portion 150, with a gap between it and both the fixing portion 120 and the frame portion 150.

[0019] The weight section 110 has a first load section 111, a second load section 112, a first beam section 113, and a second beam section 114. The first load section 111 is provided on the positive X-axis side of the fixed section 120. The second load section 112 is provided on the negative X-axis side of the fixed section 120. The first beam section 113 is provided on the positive Y-axis side of the fixed section 120. The second beam section 114 is provided on the positive Y-axis side of the fixed section 120. The end of the first load section 111 on the positive Y-axis side and the end of the second load section 112 on the positive Y-axis side are connected by the first beam section 113. The end of the first load section 111 on the negative Y-axis side and the end of the second load section 112 on the negative Y-axis side are connected by the second beam section 114.

[0020] When viewed from above, the area of ​​the first load section 111 is larger than the area of ​​the second load section 112, and the area of ​​the first beam section 113 is approximately equal to the area of ​​the second beam section 114. The dimensions of the first load section 111 in the Z-axis direction (hereinafter referred to as "thickness") are approximately uniform, and the thickness of the second load section 112, the first beam section 113, and the second beam section 114 are also similar. The thickness of the first load section 111, the second load section 112, the first beam section 113, and the second beam section 114 are approximately equal to each other. Therefore, the volume of the first load section 111 is larger than the volume of the second load section 112, and the volume of the first beam section 113 is approximately equal to the volume of the second beam section 114. Since the materials of the first load section 111, the second load section 112, the first beam section 113, and the second beam section 114 are all the same, the weight of the first load section 111 is greater than the weight of the second load section 112 by the difference in volume between the first load section 111 and the second load section 112.

[0021] The weight portion 110 has a rotation axis 119. The weight portion 110 is held relative to the housing 190 in a state that it can rotate about the rotation axis 119 as the center of rotation. The rotation axis 119 extends in the Y-axis direction and passes through the first beam portion 113 and the second beam portion 114. When the weight portion 110 rotates, the first load portion 111 is displaced in the positive or negative Z-axis direction, and the second load portion 112 is displaced in the opposite direction.

[0022] The shape of the weight when viewed from above (hereinafter referred to as "planar shape") is not limited to the rectangular frame shape described above. For example, the planar shape of the weight may be a rectangular frame with a long side extending in the Y-axis direction, or a square frame with sides extending in the X-axis and Y-axis directions. The planar shape of the weight may also be a polygonal frame, a circular frame, an elliptical frame, or a combination thereof.

[0023] The fixing portion 120 is provided at the tip of the anchor portion 176 in the lower housing 170, which will be described later. The fixing portion 120 is surrounded by the weight portion 110 with a gap in the direction of the intersecting planes. The fixing portion 120 is provided between the first vibrator 131, which will be described later, and the second vibrator 132, which will be described later, in the X-axis direction. The planar shape of the fixing portion 120 is rectangular, having a pair of short sides extending in the X-axis direction and a pair of long sides extending in the Y-axis direction. The thickness of the fixing portion 120 is approximately equal to the thickness of the weight portion 110.

[0024] The transducer 130 has a first transducer 131 and a second transducer 132. The first transducer 131 and the second transducer 132 are provided on opposite sides of the fixed part 120. The first transducer 131 is provided in the X-axis direction between the first load part 111 and the fixed part 120. The second transducer 132 is provided in the X-axis direction between the second load part 112 and the fixed part 120.

[0025] The end of the first vibrator 131 on the positive X-axis side is connected to the first load section 111, and the end of the first vibrator 131 on the negative X-axis side is connected to the fixed section 120. When the acceleration sensor 1 receives acceleration in the Z-axis direction, the position of the fixed section 120 does not change relative to the housing 190, but the weight section 110 rotates, so the position of the first load section 111 changes in the Z-axis direction relative to the housing 190. As a result, bending stress corresponding to the displacement of the first load section 111 is input to the first vibrator 131 connected to the first load section 111 and the fixed section 120. Based on this bending stress, the resonant frequency of the first vibrator 131 changes. The end of the first vibrator 131 on the positive X-axis side corresponds to one end of the first vibrator 131 in the second orthogonal axis direction, and the end of the first vibrator 131 on the negative X-axis side corresponds to the other end of the first vibrator 131 in the second orthogonal axis direction.

[0026] The end of the second transducer 132 on the negative X-axis side is connected to the second load section 112, and the end of the second transducer 132 on the positive X-axis side is connected to the fixed section 120. Similar to the first transducer 131, when the acceleration sensor 1 receives acceleration in the Z-axis direction, a bending stress corresponding to the displacement of the second load section 112 is input to the second transducer 132. Based on this bending stress, the resonant frequency of the second transducer 132 changes. The end of the second transducer 132 on the negative X-axis side corresponds to one end of the second transducer 132 in the second orthogonal axis direction, and the end of the second transducer 132 on the positive X-axis side corresponds to the other end of the second transducer 132 in the second orthogonal axis direction.

[0027] In this embodiment, the acceleration sensor is equipped with two oscillators, but it is not limited to this. The acceleration sensor may be equipped with one oscillator, or three or more oscillators.

[0028] The connecting portion 140 extends in the Y-axis direction and connects the weight portion 110 and the frame portion 150. The connecting portion 140 has a first connecting portion 143 provided on the positive Y-axis side of the fixed portion 120 and a second connecting portion 144 provided on the negative Y-axis side of the fixed portion 120. The first connecting portion 143 connects the first beam portion 113 of the weight portion 110 and the third portion 153 of the frame portion 150, which will be described later. The second connecting portion 144 connects the second beam portion 114 of the weight portion 110 and the fourth portion 154 of the frame portion 150, which will be described later. The first connecting portion 143 and the second connecting portion 144 are aligned in the Y-axis direction.

[0029] The first connecting portion 143 and the second connecting portion 144 rotatably hold the weight portion 110. The rotation axis 119 of the weight portion 110 passes through the first connecting portion 143 and the second connecting portion 144. When the acceleration sensor 1 receives acceleration and the weight portion 110 rotates, the first connecting portion 143 and the second connecting portion 144 twist, imparting a restoring force to the weight portion 110.

[0030] The frame portion 150 is provided at a distance from the weight portion 110 so as to surround the weight portion 110. The frame portion 150 is provided in the shape of a rectangular frame having a long side extending in the X-axis direction and a short side extending in the Y-axis direction. The frame portion 150 has a first portion 151 provided on the positive X-axis side of the weight portion 110, a second portion 152 provided on the negative X-axis side of the weight portion 110, a third portion 153 provided on the positive Y-axis side of the weight portion 110, and a fourth portion 154 provided on the negative Y-axis side of the weight portion 110.

[0031] The first part 151 and the second part 152 extend in the Y-axis direction, and the third part 153 and the fourth part 154 extend in the X-axis direction. The positive Y-axis end of the first part 151 is connected to the positive X-axis end of the third part 153. The negative Y-axis end of the first part 151 is connected to the positive X-axis end of the fourth part 154. The positive Y-axis end of the second part 152 is connected to the negative X-axis end of the third part 153. The negative Y-axis end of the second part 152 is connected to the negative X-axis end of the fourth part 154.

[0032] The frame portion 150 is sandwiched between the lower housing 170 and the upper housing 180. Specifically, the lower surface of the first portion 151 is joined to the first lower side wall 171 of the lower housing 170, which will be described later, and the upper surface of the first portion 151 is joined to the first upper side wall 181 of the upper housing 180, which will be described later. Similarly, the lower surface of the second portion 152 is joined to the second lower side wall 172, which will be described later, and the upper surface of the second portion 152 is joined to the second upper side wall 182, which will be described later. The lower surface of the third portion 153 is joined to the third lower side wall 173, which will be described later, and the upper surface of the third portion 153 is joined to the third upper side wall 183, which will be described later. The lower surface of the fourth portion 154 is joined to the fourth lower side wall 174, which will be described later, and the upper surface of the fourth portion 154 is joined to the fourth upper side wall 184, which will be described later.

[0033] As shown in Figure 1, the lower housing 170 is provided in a box shape that opens towards the upper housing 180. The lower housing 170 has a lower main wall 175, a first lower side wall 171, a second lower side wall 172, a third lower side wall 173, a fourth lower side wall 174, and an anchor portion 176.

[0034] The lower main wall 175 is a flat plate-like portion having a main surface extending in the XY plane. The planar shape of the lower main wall 175 is rectangular, having a pair of long sides extending in the X-axis direction and a pair of short sides extending in the Y-axis direction. The first lower side wall 171 extends from the end of the lower main wall 175 on the positive X-axis side toward the first portion 151 of the frame portion 150 in the device layer 100. Similarly, the second lower side wall 172 extends from the end of the lower main wall 175 on the negative X-axis side toward the second portion 152 of the frame portion 150. The third lower side wall 173 extends from the end of the lower main wall 175 on the positive Y-axis side toward the third portion 153 of the frame portion 150. The fourth lower side wall 174 extends from the end of the lower main wall 175 on the negative Y-axis side toward the fourth portion 154 of the frame portion 150.

[0035] The anchor portion 176 protrudes from the center of the lower main wall 175 toward the positive Z-axis direction. The anchor portion 176 is provided at a distance from the first lower side wall 171, the second lower side wall 172, the third lower side wall 173, and the fourth lower side wall 174, and is surrounded by the first lower side wall 171, the second lower side wall 172, the third lower side wall 173, and the fourth lower side wall 174 in the direction of intersecting planes. The shape of the anchor portion 176 is a rectangular prism, and the planar shape of the anchor portion 176 is a rectangle having a pair of long sides extending in the Y-axis direction and a pair of short sides extending in the X-axis direction. A fixing portion 120 is provided at the tip of the anchor portion 176, and the anchor portion 176 fixes the position of the fixing portion 120 relative to the lower housing 170.

[0036] As shown in Figure 1, the upper housing 180 is provided in a box shape that opens towards the lower housing 170. The upper housing 180 has an upper main wall 185, a first upper side wall 181, a second upper side wall 182, a third upper side wall 183, and a fourth upper side wall 184.

[0037] The upper main wall 185 is a flat plate-like portion having a main surface extending in the XY plane. The planar shape of the upper main wall 185 is rectangular, having a pair of long sides extending in the X-axis direction and a pair of short sides extending in the Y-axis direction. The first upper side wall 181 extends from the end of the upper main wall 185 on the positive X-axis side toward the first portion 151 of the frame portion 150 in the device layer 100. Similarly, the second upper side wall 182 extends from the end of the upper main wall 185 on the negative X-axis side toward the second portion 152 of the frame portion 150. The third upper side wall 183 extends from the end of the upper main wall 185 on the positive Y-axis side toward the third portion 153 of the frame portion 150. The fourth upper side wall 184 extends from the end of the upper main wall 185 on the negative Y-axis side toward the fourth portion 154 of the frame portion 150.

[0038] Next, the layer structure of the device layer 100 will be described. As shown in Figures 3 and 4, the device layer 100 has a first layer 101 and a second layer 102. The first layer 101 and the second layer 102 are stacked in the Z-axis direction. The first layer 101 is provided on the upper housing 180 side, and the second layer 102 is provided on the lower housing 170 side. The first layer 101 is provided over the entire device layer 100, that is, over the weight portion 110, the fixing portion 120, the vibrator 130, the connecting portion 140, and the frame portion 150. The second layer 102 is provided over the weight portion 110, the fixing portion 120, the connecting portion 140, and the frame portion 150, excluding the vibrator 130. In other words, the weight portion 110, the fixing portion 120, the connecting portion 140, and the frame portion 150 are provided by the first layer 101 and the second layer 102, but the vibrator 130 is provided by the first layer 101 only. Therefore, the thickness of the vibrator 130 is smaller than the thickness of each of the weight portion 110, the fixing portion 120, the connecting portion 140, and the frame portion 150.

[0039] Next, with reference to Figures 5 to 9, the more detailed configuration of the device layer 100 and its behavior during acceleration detection will be described. Figure 5 is a cross-sectional view of the device layer 100 in its basic state. Figure 6 is a cross-sectional view of the device layer 100 in its detection state. Figure 7 is a diagram showing the simulation results of the stress distribution in the first embodiment. Figure 8 is a cross-sectional view of the device layer according to the comparative example in its detection state. Figure 9 is a diagram showing the simulation results of the stress distribution in the comparative example. "Detection state" refers to the state in which the weight portion 110 is rotating due to receiving acceleration in the direction of the sensitivity axis.

[0040] As shown in Figure 5, the first layer 101 has an upper surface 101A provided on the upper housing 180 side and a lower surface 101B provided on the lower housing 170 side. The second layer 102 has an upper surface 102A provided on the upper housing 180 side and a lower surface 102B provided on the lower housing 170 side. The first transducer 131 has an upper surface 131A provided on the upper housing 180 side, a lower surface 131B provided on the lower housing 170 side, and a neutral surface 131C for bending stress input to the first transducer 131. The second transducer 132 has an upper surface 132A provided on the upper housing 180 side, a lower surface 132B provided on the lower housing 170 side, and a neutral surface 132C for bending stress input to the second transducer 132.

[0041] In the basic state, the upper surfaces 131A, 132A, lower surfaces 131B, 132B, and neutral surfaces 131C, 132C extend in the XY plane direction. Since the oscillator 130 consists only of the first layer 101, the upper surfaces 131A, 132A are provided by the upper surface 101A of the first layer 101, and the lower surfaces 131B, 132B are provided by the lower surface 101B of the first layer 101. The neutral surface 131C is located midway between the upper surface 131A (upper surface 101A) and the lower surface 131B (lower surface 101B). The neutral surface 132C is located midway between the upper surface 132A (upper surface 101A) and the lower surface 132B (lower surface 101B).

[0042] Since the weight portion 110, the fixing portion 120, the connecting portion 140, and the frame portion 150 are made up of a first layer 101 and a second layer 102, the lower surfaces of the weight portion 110, the fixing portion 120, the connecting portion 140, and the frame portion 150 are provided by the lower surface 102B of the second layer 102, and the upper surfaces of the weight portion 110, the fixing portion 120, the connecting portion 140, and the frame portion 150 are provided by the upper surface 101A of the first layer 101. In the basic state, the upper surfaces of the weight portion 110, the fixing portion 120, the connecting portion 140, and the frame portion 150 are located on the same intersecting plane as the upper surfaces 131A, 132A of the vibrator 130, but the lower surfaces of the weight portion 110, the fixing portion 120, the connecting portion 140, and the frame portion 150 are located closer to the lower housing 170 than the lower surfaces 131B, 132B of the vibrator 130.

[0043] The rotation axis 119 of the weight portion 110 passes through the center of the ZX cross-section of the connecting portion 140. Since the oscillator 130 consists only of the first layer 101, and the connecting portion 140 consists of the first layer 101 and the second layer 102, the rotation axis 119 is located away in the Z-axis direction from the extension planes extending in the XY direction from the neutral planes 131C, 132C. Let h1 be the thickness of the oscillator 130, i.e., the thickness of the first layer 101. Let h2 be the thickness of the connecting portion 140, i.e., the sum of the thickness of the first layer 101 and the thickness of the second layer 102. When the relationship h1 < 0.5 × h2 holds, the rotation axis 119 is located further away in the Z-axis direction from the extension planes of the neutral planes 131C, 132C, and away in the negative Z-axis direction from the extension planes extending in the XY direction from the lower planes 131B, 132B. In other words, the rotation axis 119 is located away in the Z-axis direction from the region extending from the oscillator 130 in the XY plane direction. At this time, the rotation axis 119 passes through the second layer 102.

[0044] As shown in Figure 6, when acceleration in the positive Z-axis direction is detected, the weight portion 110 rotates around the rotation axis 119 as the center of rotation, causing the first load portion 111 to be displaced in the positive Z-axis direction and the second load portion 112 to be displaced in the negative Z-axis direction. The first vibrator 131 undergoes bending deformation based on the bending stress input by the first load portion 111, resulting in compressive or tensile strain in the first vibrator 131. The second vibrator 132 undergoes bending deformation based on the bending stress input by the second load portion 112, resulting in compressive or tensile strain in the second vibrator 132. The strain occurring in the first vibrator 131 is in opposite phase to the strain occurring in the second vibrator 132.

[0045] The device layer 900 according to the comparative example shown in FIGS. 8 and 9 is different from the device layer 100 according to the first embodiment in that the weight portion 910 (the first load portion 911 and the second load portion 912), the fixing portion 920, and the vibrators 930 (the first vibrator 931 and the second vibrator 932) are provided by the same layer and their respective thicknesses are substantially equal. Although not shown, the neutral plane with respect to the bending stress input to the first vibrator 931 and the neutral plane with respect to the bending stress input to the second vibrator 932 are located on a plane including the rotation axis 919 of the weight portion 910 in the basic state. That is, the rotation axis 919 of the weight portion 910 is not separated from the neutral plane of the first vibrator 931 and the neutral plane of the second vibrator 932 in the sensitivity axis direction.

[0046] As shown in the first embodiment in Figures 5 and 6, when the rotation axis 119 is located below the lower surfaces 131B and 132B in the basic state, in the detection state, the strain generated on the upper surface 131A of the first vibrator 131 is in phase with the strain generated on the lower surface 131B, and the strain generated on the upper surface 132A of the second vibrator 132 is in phase with the strain generated on the lower surface 132B. As shown in the comparative example in Figure 8, when the rotation axis 919 of the weight portion 910 is located on the extension of the neutral plane of the vibrator 930, in the detection state, as shown in Figure 9, out-of-phase strain occurs on the upper and lower surfaces of the vibrator 930, so the strains of the vibrator 930 as a whole cancel each other out. For this reason, in the comparative example shown in Figure 8, since the strain of the vibrator 930 is small, the change in the resonant frequency corresponding to the strain is small, and it becomes difficult to detect acceleration by measuring the change in resonant frequency. However, as shown in Figure 7, in the device layer 100 of this embodiment, the strain on the upper surface 131A side and the strain on the lower surface 131B side of the first vibrator 131 do not cancel each other out, resulting in a large overall strain on the first vibrator 131. Consequently, the change in the resonant frequency of the first vibrator 131 becomes large, making it possible to detect acceleration based on the change in the resonant frequency of the first vibrator 131. The same applies to the second vibrator 132. As shown in Figure 7, since the first vibrator 131 and the second vibrator 132 are distorted in opposite phases, the resonant frequency of the first vibrator 131 changes in the opposite direction to the resonant frequency of the second vibrator 132. Therefore, by differentially detecting the changes in the resonant frequencies of the first vibrator 131 and the second vibrator 132, the detection sensitivity of the acceleration sensor 1 can be improved.

[0047] In the basic state, when the rotation axis 119 is located between the extended planes of the neutral planes 131C and 132C and the extended planes of the lower planes 131B and 132B, the strain generated on the upper surface 131A and the strain generated on the lower surface 131B of the first oscillator 131 are in opposite phases, but the amount of strain that cancels out between the upper surface 131A and the lower surface 131B is reduced. Therefore, even in this case, the overall strain of the oscillator in the detection state is greater than when the rotation axis is located on the extended plane of the neutral plane, and it becomes possible to detect acceleration in the Z-axis direction.

[0048] As described above, according to the present embodiment, when in the basic state, the rotation axis 119 of the weight portion 110 is separated in the Z-axis direction from the extension planes of the neutral planes 131C and 132C.

[0049] According to this, it is possible to suppress the cancellation of the strain on the upper surface side and the lower surface side of the vibrator 130 in the detection state, and increase the strain in the entire vibrator 130. Therefore, the change in the resonance frequency according to the strain becomes easier to detect, and the acceleration in the Z-axis direction can be detected.

[0050] Further, in the present embodiment, the thickness of the fixing portion 120 is larger than the thickness of the vibrator 130.

[0051] According to this, it is possible to adjust how much the extension planes of the neutral planes 131C and 132C and the rotation axis 119 are separated from each other according to the thickness of the fixing portion 120. The further the rotation axis 119 is separated from the extension planes of the neutral planes 131C and 132C, the more the sensitivity of the acceleration sensor 1 is improved.

[0052] Further, in the present embodiment, the thickness of the weight portion 110 is larger than the thickness of the vibrator 130.

[0053] According to this, since the weight of the weight portion 110 increases, the displacement of the weight portion 110 in the detection state can be increased. The larger the displacement of the weight portion 110, the larger the strain of the vibrator 130, and thus the larger the change in the resonance frequency of the vibrator 130. Therefore, the detection sensitivity of the acceleration sensor 1 is improved.

[0054] Further, in the present embodiment, the vibrator 130 has a first vibrator 131 and a second vibrator 132 provided on opposite sides with respect to the fixing portion 120.

[0055] According to this, since the first vibrator 131 and the second vibrator 132 are strained in opposite phases in the detection state, the detection sensitivity of the acceleration sensor 1 is improved by differentially detecting the first vibrator 131 and the second vibrator 132.

[0056] Further, in the present embodiment, the rotation axis 119 of the weight portion 110 is separated in the Z-axis direction from the region where the vibrator 130 extends in the XY-plane direction.

[0057] According to this, the strain on the upper surface and the strain on the lower surface of the vibrator 130 become in phase, further increasing the overall strain of the vibrator 130. Consequently, the change in the resonant frequency of the vibrator 130 becomes larger, improving the detection sensitivity of the acceleration sensor 1.

[0058] Other embodiments are described below. Components identical or similar to those shown in the first embodiment are denoted by the same or similar reference numerals, and their descriptions are omitted as appropriate. Furthermore, similar effects and benefits from similar components are not mentioned sequentially.

[0059] <Second Embodiment> The configuration of the device layer 200 according to the second embodiment will be described with reference to Figure 10. Figure 10 is a cross-sectional view of the device layer 200 according to the second embodiment.

[0060] The portion of the device layer 200 excluding the resonator 230 is provided by the first layer 201 and the second layer 202, while the resonator 230 is provided only by the second layer 202. The rotation axis 219 is located away from the anchor portion 176 from the extended planes of the neutral plane 231C of the first resonator 231 and the neutral plane 232C of the second resonator 232. The rotation axis 219 passes through the first layer 201.

[0061] <Third Embodiment> The configuration of the acceleration sensor 3 according to the third embodiment will be described with reference to Figures 11 and 12. Figure 11 is a cross-sectional view of the acceleration sensor 3 according to the third embodiment. Figure 12 is a cross-sectional view of the acceleration sensor 3 according to the third embodiment.

[0062] The device layer 300 of the acceleration sensor 3 further comprises a third layer 303 in addition to the first layer 301 and the second layer 302. The first layer 301, the second layer 302, and the third layer 303 are stacked in this order. The weight portion 310, the fixing portion 320, and the frame portion 350 are provided by the first layer 301, the second layer 302, and the third layer 303. The vibrator 330 is provided by the first layer 301 only. The connecting portion 340 is provided by the third layer 303 only. Therefore, the thickness of the connecting portion 340 is smaller than the thickness of the weight portion 310, the fixing portion 320, and the frame portion 350, respectively.

[0063] In the basic state, the connecting portion 340 is located in the Z-axis direction away from the region extending from the oscillator 330 in the XY plane. The rotation axis 319 of the weight portion 310 passes through the connecting portion 340 that rotatably holds the weight portion 310, and the connecting portion 340 through which the rotation axis 319 passes is provided only by the third layer 303. Therefore, the rotation axis 319 passes through the third layer 303.

[0064] According to this embodiment, the rotating shaft 319 moves further away from the vibrator 330, which further increases the overall distortion of the vibrator 330. Consequently, the change in the resonant frequency of the vibrator 330 becomes larger, improving the detection sensitivity of the acceleration sensor 3.

[0065] <Fourth Embodiment> The configuration of the acceleration sensor 4 according to the fourth embodiment will be described with reference to Figures 13 and 14. Figure 13 is a plan view of the acceleration sensor according to the fourth embodiment in the basic state. Figure 14 is a plan view of the acceleration sensor according to the fourth embodiment in the detection state.

[0066] The device layer 400 of the acceleration sensor 4 has a first sensor structure 400a and a second sensor structure 400b. The first sensor structure 400a and the second sensor structure 400b are aligned in the Y-axis direction. The first sensor structure 400a is provided on the positive Y-axis side of the second sensor structure 400b.

[0067] The first sensor structure 400a has a weight portion 410a, a fixed portion 420a, and a vibrator 430a. The second sensor structure 400b has a weight portion 410b, a fixed portion 420b, and a vibrator 430b. The weight portion 410a is an example of the first weight portion, and the weight portion 410b is an example of the second weight portion. The fixed portion 420a is an example of the first fixed portion, and the fixed portion 420b is an example of the second fixed portion. The weight portion 410a has a first load portion 411a provided on the positive X-axis side of the fixed portion 420a, and a second load portion 412a provided on the negative X-axis side of the fixed portion 420a. The weight portion 410b has a third load portion 411b provided on the positive X-axis side of the fixed portion 420b and a fourth load portion 412b provided on the negative X-axis side of the fixed portion 420b. The vibrator 430a has a first vibrator 431a provided between the fixed portion 420a and the first load portion 411a and a second vibrator 432a provided between the fixed portion 420a and the second load portion 412a. The vibrator 430b has a third vibrator 431b provided between the fixed portion 420b and the third load portion 411b and a fourth vibrator 432b provided between the fixed portion 420b and the fourth load portion 412b.

[0068] The first connecting portion 443, the second connecting portion 444, the third connecting portion 445, and the fixing portions 420a and 420b are aligned in the Y-axis direction. The weight portion 410a is connected to the third portion 153 of the frame portion 150 by the first connecting portion 443. The weight portion 410b is connected to the fourth portion 154 of the frame portion 150 by the second connecting portion 444. The weight portions 410a and 410b are connected to each other by the third connecting portion 445.

[0069] The weights 410a and 410b are configured to rotate in opposite directions when detected. Specifically, in weight 410a, the weight of the first load portion 411a is less than the weight of the second load portion 412a, and in weight 410b, the weight of the third load portion 411b is greater than the weight of the fourth load portion 412b.

[0070] In this embodiment, the acceleration sensor 4 detects acceleration based on the difference {(f1-f2)-(f3-f4)} between the difference (f1-f2) between the resonant frequency f1 of the first vibrator 431a and the resonant frequency f2 of the second vibrator 432a in the first sensor structure 400a, and the difference (f3-f4) between the resonant frequency f3 of the third vibrator 431b and the resonant frequency f4 of the fourth vibrator 432b in the second sensor structure 400b.

[0071] As shown in Figure 14, when the acceleration sensor 4 receives acceleration in the negative X-axis direction, the weight portion 410a is displaced in the negative X-axis direction relative to the fixed portion 420a, and the weight portion 410b is displaced in the positive X-axis direction relative to the fixed portion 420b. As a result, in the first sensor structure 400a, compressive strain occurs in the first vibrator 431a and tensile strain occurs in the second vibrator 432a. Similarly, in the second sensor structure 400b, compressive strain occurs in the third vibrator 431b and tensile strain occurs in the fourth vibrator 432b. If the resonant frequency in the basic state of each vibrator is f0, and the change in resonant frequency when subjected to acceleration in the negative X-axis direction is Δfx, then it can be expressed as follows: f1 = f0 + Δf f2 = f0 - Δf f3 = f0 + Δf f4 = f0 - Δf

[0072] Therefore, the differences f1 - f2 and f3 - f4 are expressed by the following equations: f1 - f2 = (f0 + Δf) - (f0 - Δf) = 2 × f0 f3 - f4 = (f0 + Δf) - (f0 - Δf) = 2 × f0 Thus, the difference of the differences {(f1 - f2) - (f3 - f4)} is 0, as shown in the following equation, and cancels out: {(f1 - f2) - (f3 - f4)} = 2 × f0 - 2 × f0 = 0

[0073] As described above, according to this embodiment, the acceleration sensor 4 can suppress sensitivity in other axes and improve the detection accuracy of acceleration in the sensitivity axis direction.

[0074] As described above, according to one aspect of the present invention, an acceleration sensor capable of detecting acceleration in the out-of-plane direction can be provided.

[0075] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. The present invention can be modified or improved without departing from its spirit, and equivalents thereof are also included. That is, embodiments and / or modifications made by those skilled in the art are also included in the scope of the present invention, as long as they retain the features of the present invention. For example, the elements and their arrangement, materials, conditions, shapes, sizes, etc., of the embodiments and / or modifications are not limited to those exemplified and can be modified as appropriate. Furthermore, the embodiments and modifications are illustrative, and it goes without saying that partial substitution or combination of the configurations shown in different embodiments and / or modifications is possible, and these are also included in the scope of the present invention as long as they retain the features of the present invention.

[0076] 1...Accelerometer 100...Device layer 110...Weight section 111...First load section 112...Second load section 113...First beam section 114...Second beam section 119...Rotation shaft 120...Fixed section 130...Vibrator 131...First vibrator 132...Second vibrator 140...Connecting section 141...First connecting section 142...Second connecting section 150...Frame section 151...First part 152...Second part 153...Third part 154...Fourth part 170...Lower housing 176...Anchor section 180...Upper housing 190...Housing

Claims

1. An acceleration sensor for detecting acceleration in the direction of the sensitivity axis, comprising a device layer including a weight portion, a fixed portion, and a vibrator, each arranged on an intersecting plane intersecting the sensitivity axis direction, and a housing for housing the device layer, wherein the weight portion has a rotation axis extending in a first orthogonal axis direction perpendicular to the sensitivity axis direction, and is held in the housing so as to rotate about the rotation axis when subjected to acceleration in the direction of the sensitivity axis direction, the fixed portion is fixed to the housing via an anchor portion protruding from the housing in the direction of the sensitivity axis direction, the vibrator is connected to the weight portion at one end in the direction of the sensitivity axis direction and a second orthogonal axis direction perpendicular to the first orthogonal axis direction, and is connected to the fixed portion at the other end opposite to the one end in the second orthogonal axis direction, and is configured such that its resonant frequency changes based on the bending stress corresponding to the displacement of the weight portion, and when the weight portion is in a stationary state, the rotation axis of the weight portion is away in the direction of the sensitivity axis direction from a plane extending along the intersecting plane from the neutral plane of the vibrator with respect to the bending stress.

2. The acceleration sensor according to claim 1, wherein the thickness of the fixed portion in the sensitivity axis direction is greater than the thickness of the vibrator in the sensitivity axis direction.

3. The acceleration sensor according to claim 1 or 2, wherein the thickness of the weight portion in the sensitivity axis direction is greater than the thickness of the oscillator in the sensitivity axis direction.

4. The acceleration sensor according to any one of claims 1 to 3, wherein the vibrator comprises a first vibrator and a second vibrator provided on the opposite side of the fixed portion from the first vibrator.

5. When the weight portion is in a stationary state, the rotation axis of the weight portion is located away in the direction of the sensitivity axis from the region extending from the vibrator along the intersecting surface, according to any one of claims 1 to 4.

6. The acceleration sensor according to any one of claims 1 to 5, wherein the device layer further has a connecting portion that extends in the first orthogonal axis direction and connects the weight portion to the housing, the thickness of the connecting portion in the sensitivity axis direction is smaller than the thickness of the weight portion in the sensitivity axis direction, and when the weight portion is in a stationary state, the connecting portion is separated in the sensitivity axis direction from the region extending from the vibrator along the intersecting surface.

7. The weight portion has a first weight portion and a second weight portion arranged side by side in the first orthogonal axis direction, the fixing portion has a first fixing portion and a second fixing portion arranged side by side in the first orthogonal axis direction, the vibrator has a first vibrator and a second vibrator connected to the first weight portion and the first fixing portion and arranged side by side in the second orthogonal axis direction with the first fixing portion in between, and a third vibrator and a fourth vibrator connected to the second weight portion and the second fixing portion and arranged side by side in the second orthogonal axis direction with the second fixing portion in between, the device layer further has a first connecting portion, a second connecting portion and a third connecting portion arranged side by side in the first orthogonal axis direction, the first connecting portion extends in the first orthogonal axis direction and connects the first weight portion to the housing, the second connecting portion extends in the first orthogonal axis direction and connects the second weight portion to the housing, the third connecting portion extends in the first orthogonal axis direction and connects the first weight portion and the second weight portion. The acceleration sensor according to any one of claims 1 to 6.

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